The present invention relates to a photographic zoom lens system, and more particularly to an inexpensive and compact telephoto zoom lens system that features a zoom ratio on the order of 3.
A number of telephoto zoom lens systems that feature zoom ratios on the order of 3 have been proposed in the prior art. For example, JP-A-60-60617 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describes a version that is composed of a small number of lens elements and which is inexpensive, whereas JP-A-61-241719 describes a version that is compact and low in cost.
Although the two prior art versions of zoom lens systems described above are intended to be available at low cost, they still have problems. The zoom lens system proposed in JP-A-60-60617 is composed of only eleven elements but is somewhat bulky due to the zooming method adopted. In contrast, the version proposed in JP-A-61-241719 adopts a compact zooming system. However, in order to reduce the number of lens elements to as few as eleven, an optical material having a high refractive index must be employed at the penalty of increased cost.